This invention relates generally to blowout preventers for closing about a pipe or other objects in the bore or across an open bore of a housing mounted on a wellhead. More particularly, it relates to improvements in ram type blowout preventers wherein rams are slidable within guideways extending radially from the bore between inner positions to engage one another to close the bore and outer positions to open the bore.
Conventionally, bonnets are mounted on the body for movement between positions opening and closing the outer ends of the guideways to permit the rams to be installed within or removed from the guideways. Hydraulic operators mounted on the bonnets include a rod extending through the bonnet for connection with the rams. The bonnets may be hinged to the body for swinging between opened and closed positions, or they may be so moved by the hydraulic operators. In either case, the inner faces of the bonnets are forced into tight engagement with the outer faces of the body by bolts connecting the bonnet to the body.
Packings are carried on the inner face of the bonnet to sealably engage the outer face of the body in an effort to contain the fluid pressure in the preventer bore, and thus in the guideways. As a practical matter, however, neither face is perfectly flat so that there are gaps between them even when forced against one another as the bolts are made up. Also, the fluid pressure in the preventer may be so high as to cause the bonnet to bend outwardly, thus tending to create even greater gaps between the faces into which the packing may extrude, in addition to those gaps which normally result from deflection of the bolts due to the internal pressure, whereby the large gaps which occur because of deflection are very difficult to seal under conditions of high/low temperatures and high pressure. As a result, it has been the practice to make up the bolts with greater and greater torque, all of which is time-consuming. Furthermore, many preventer bodies and bonnets are of such configuration that they cannot be connected by a full circle of bolts, thus leaving potential leak paths.
The object of this invention is to provide a ram type blowout preventer of the type described in which the body and bonnet faces are so sealed with respect to one another as to overcome these and other problems; and, more particularly, to provide such a preventer having means for sealing between the faces which is of such construction as to eliminate gaps between the faces of the bonnet and body through which leaks might occur without having to overtorque the bolts.
These and other objects are accomplished, in accordance with the illustrated and preferred embodiment of the invention, by a ram type blowout preventor of the type described in which the bonnet has a recess in its inner face to form a peripheral wall and an end wall opposite the outer face of the body when the bonnet is closed, and a metal ring mounted on the bonnet for limited axial and radial movement within the recess carriers a first elastomeric ring on its inner side for sealing against the face of the body. Means such as a spring acts between the inner wall of the recess and the metal ring to yieldably urge the inner side of the metal ring toward said outer face of the bonnet, and a second elastomeric ring is carried about the outer periphery of the metal ring for sealing against the peripheral wall of the recess about an area which is greater than the area of the sealing engagement of the first elastomeric ring with the bonnet face and spaced outwardly therefrom, whereby fluid pressure in the guideway is effective to urge the metal ring toward the outer bonnet face and at the same time expand its outer circumference toward said peripheral wall of the recess. More particularly, the metal ring is of such construction that its inner side is tightly engaged against the outer face of the body prior to radial expansion of the ring periphery thereof and tightly against the peripheral wall of the recess, thus assuring that gaps between the body and bonnet surfaces are closed to prevent extrusion of the elastomeric rings between them.
In the illustrated embodiment of the invention, the metal ring has holes extending therethrough from its inner to its outer sides, and bolts extend loosely through the holes and into the end wall of the recess and have enlarged outer ends to retain the metal ring on the bonnet while permitting it to move limited distances radially as well as axially of the bolts.